One of the first paid ones was Crazy Machines a puzzle game where you have to solve rube goldberg machines, i must have been around 8. I only know about this now because I have only recently dusted off the old PC I was playing on. Its fun, I like that they always added a small backstory to every puzzle. The puzzles I have created were no real puzzles and I have just built what I felt like building. Definitely worth it (the newer ones not so much.)